Manual Page Search Parameters
POSIX_FALLOCATE(2) System Calls Manual POSIX_FALLOCATE(2)

posix_fallocate — pre-allocate storage for a range in a file

Standard C Library (libc, -lc)

#include <fcntl.h>

int
posix_fallocate(int fd, off_t offset, off_t len);

Required storage for the range offset to offset + len in the file referenced by fd is guaranteed to be allocated upon successful return. That is, if () returns successfully, subsequent writes to the specified file data will not fail due to lack of free space on the file system storage media. Any existing file data in the specified range is unmodified. If offset + len is beyond the current file size, then posix_fallocate() will adjust the file size to offset + len. Otherwise, the file size will not be changed.

Space allocated by () will be freed by a successful call to creat(2) or open(2) that truncates the size of the file. Space allocated via posix_fallocate() may be freed by a successful call to ftruncate(2) that reduces the file size to a size smaller than offset + len.

If successful, posix_fallocate() returns zero. It returns an error on failure, without setting errno.

Possible failure conditions:

[]
The fd argument is not a valid file descriptor.
[]
The fd argument references a file that was opened without write permission.
[]
The value of offset + len is greater than the maximum file size.
[]
A signal was caught during execution.
[]
The len argument was less than or equal to zero, the offset argument was less than zero, or the operation is not supported by the file system.
[]
An I/O error occurred while reading from or writing to a file system.
[]
Corrupted data was detected while reading from the file system.
[]
The fd argument does not refer to a file that supports posix_fallocate.
[]
There is insufficient free space remaining on the file system storage media.
[]
The file descriptor fd has insufficient rights.
[]
The fd argument is associated with a pipe or FIFO.

creat(2), ftruncate(2), open(2), unlink(2)

The posix_fallocate() system call conforms to IEEE Std 1003.1-2004 (“POSIX.1”).

The posix_fallocate() function appeared in FreeBSD 9.0.

posix_fallocate() and this manual page were initially written by Matthew Fleming <mdf@FreeBSD.org>.

March 30, 2020 dev